BACKGROUND: Refined sugars (e.g., sucrose, fructose) were absent in the diet of
most people until very recently in human history. Today overconsumption of diets
rich in sugars contributes together with other factors to drive the current
obesity epidemic. Overconsumption of sugar-dense foods or beverages is initially
motivated by the pleasure of sweet taste and is often compared to drug addiction.
Though there are many biological commonalities between sweetened diets and drugs
of abuse, the addictive potential of the former relative to the latter is
currently unknown.
METHODOLOGY/PRINCIPAL FINDINGS: Here we report that when rats were allowed to
choose mutually-exclusively between water sweetened with saccharin-an intense
calorie-free sweetener-and intravenous cocaine-a highly addictive and harmful
substance-the large majority of animals (94%) preferred the sweet taste of
saccharin. The preference for saccharin was not attributable to its unnatural
ability to induce sweetness without calories because the same preference was also
observed with sucrose, a natural sugar. Finally, the preference for saccharin was
not surmountable by increasing doses of cocaine and was observed despite either
cocaine intoxication, sensitization or intake escalation-the latter being a
hallmark of drug addiction.
CONCLUSIONS: Our findings clearly demonstrate that intense sweetness can surpass
cocaine reward, even in drug-sensitized and -addicted individuals. We speculate
that the addictive potential of intense sweetness results from an inborn
hypersensitivity to sweet tastants. In most mammals, including rats and humans,
sweet receptors evolved in ancestral environments poor in sugars and are thus not
adapted to high concentrations of sweet tastants. The supranormal stimulation of
these receptors by sugar-rich diets, such as those now widely available in modern
societies, would generate a supranormal reward signal in the brain, with the
potential to override self-control mechanisms and thus to lead to addiction.